This invention relates generally to an air-conditioner using as a working medium a refrigerant which does not contain chlorine, and less affects the environment of the earth, and more particular to an air-conditioner of the heat pump type in which there is used a working medium composed of a mixture of not less than two kinds of refrigerants containing no chlorine.
In a heat pump-type air-conditioner, during a cooling operation, an interior heat exchanger is used as an evaporator, and an exterior heat exchanger is used as a condenser, whereas during a heating operation, the interior heat exchanger is used as a condenser, and the exterior heat exchanger is used as an evaporator.
As such interior and exterior heat exchangers, there has been used, for example, a heat exchanger of the cross fin tube type as disclosed in Japanese Patent Examined Publication No. 4-45753, in which a number of fins are provided at predetermined intervals in juxtaposed relation, and a plurality of heat transfer tubes extend perpendicularly through these fins in such a manner that these heat transfer tubes are arranged in a staggered manner as a whole. As such a heat transfer tube, a tube with a groove formed in its inner surface, as disclosed in Japanese Patent Unexamined Publication No. 4-260792, has been extensively used.
When instead of a conventional refrigerant HCFC22 (Abbreviation of Hydro chloro fluoro carbon 22), a non-azeotrope refrigerant, composed of a mixture of not less than two kinds of refrigerants having no chlorine, is used in a conventional air-conditioner, the cooling medium components of a lower boiling point first evaporate within an evaporator under an operating condition in which the same average evaporation temperature is obtained. Therefore, the refrigerant evaporation temperature becomes the lowest at an inlet of the evaporator. This results in a problem that during a heating operation, frost is liable to deposit locally at an inlet portion of an exterior heat exchanger, so that the heating ability is lowered.